Drewy, what you describe is maybe 2% of facebook. Facebook is having on many websites their trackers, which allows them to connect your - limited in use, protected account - to your entire digital live. They know which bank you use, which websites you visit, at which company you work and they have probably your entire addressbook since you (assumption here) use whatsapp. They know what time you awake and what time you go asleep. They know what television programs you watch, what music you like. This all is not directly harmful, but I can imagine more harmful things.
Facebook knows more about my wife than I do, and facebook probably knows more about me than I do.
This also counts for you, of course.
The point is that Mark Z is having the biggest treasure on this planet (significant data about 2 billion people), and he is trying to keep it for himself like the King-under-the-Mountain, but the company starts to be to big to fail and certain institutions, like the US government start to be aware that he might not be the best guy to manage it.
If wrong people start to have access to the data, people could blackmail other people. The effects on e.g. local politics can be huge this way. If some smart bloke distills a list of all gay people in a 'scientific' program, and this data gets to Saudi Arabia or Iran, certain people could ultimately be death sentenced in these countries.
Facebook is just another way of a social-control and rating system like the Chinese now try to implement theirselves.